The production of nanoamorphous dispersions of photographically useful compounds is described in U.S. Pat. No. 2,322,027 and in German Patent DD 299 608. Such dispersions are prepared by mechanical dispersion wherein the hydrophobic photographically useful compound is dissolved in a mixture of low-boiling and high-boiling solvents and this solution is then dispersed as an aqueous colloid solution by means of high speed stirring in the presence of surfactants.
Peterson and Weissberger, in U.S. Pat. No. 2,353,262, disclose that noncoupling compounds having a benzoylbenzene group, a sulfonamide group, or an alkyl group of at least 5 carbon atoms are useful in preventing crystallization of a coupler normally tending to crystallize and having a benzoylbenzene group and/or a benzoylacetamino group. Godowsky and Duane, in U.S. Pat. No. 2,870,012, disclose a solvent-shifting process for preparing microdispersions of color coupler compounds comprising at least one acid group (carboxyl or sulfonic acid).
Townsley and Trunley, in U.K. Pat. No. 1,193,349, disclose a solvent-shifting and pH-shifting process in the presence of a protective colloid for dispersing couplers as amorphous colloidal dispersions. Their process is applied to couplers that have no sulphonic acid or carboxylic acid solubilizing groups and that are soluble in a mixture of water-miscible organic solvent and aqueous alkali.
Kroha et al., in Patentschrift 138 831, disclose how photographically useful compounds rendered soluble as the result of substitution with sulfo groups, carboxyl groups, and the like, are generally present in a microcrystalline state when precipitated in aqueous gelatin solutions.
Sakamoto et al., in U.S. Pat. No. 3,700,454, disclose that conventionally prepared dispersions of certain couplers, prepared with a water-immiscible high boiling solvent, occasionally crystallize during the dispersing step or thereafter, with the result that the photographic properties of the light-sensitive material are greatly deteriorated. They also indicate, however, that control of such unwanted crystallization is difficult to achieve and that the coupler cannot sufficiently be prevented from crystallization.
Van Doorselaer et al. in U.S. Pat. No. 3,658,546, disclose that dispersions of water-insoluble photographic components with or without hydrophilic colloids form nanoamorphous dispersion that are stable enough to be stored. Nitttel and Reckziegel disclose in U.S. Pat. No. 3,689,271 that the emulsification of additives into a photographic element is stabilized by combining the additive with certain secondary carboxcylic acids before they are emulsified. These additive are indicated as having a pronounced tendency to prevent crystallization of couplers dispersed by emulsification.
Iwama et al., in U.S. Pat. No. 3,658,545, disclose that undesired crystallization occurs with certain classes of photographic couplers in combination with coupler solvents. Plaschnick et al., in U.S. Pat. No. 4,410,624, disclose that acid amides, phthalic acid esters, and phosphate esters have been found effective as solvents for couplers and that these solvents prevent crystallization manifestations. Deleterious effects of crystallization of photographically useful compounds are disclosed by M ader et al. in Offenlegungsschrift DE 4,000,844 A1. Tsukahara and Kobayashi, in U.S. Pat. No. 5,192,651, disclose that couplers which have a p-cyano-phenylureido group in the 2-position and a ballast group in the 5-position generally suffer from the disadvantage that they readily precipitate.
Nakamura et al., in U.S. Pat. No. 3,881,020, disclose a process of preparing aqueous suspensions of chlorampenicol palmitate to obtain fine and uniform alpha-type crystals having high bioactivity. Nakamura et al. teach that such fine and uniform crystals could never be obtained by any ordinary mechanical milling or conventional process, and they also teach methods of obtaining amorphous crystals.
Langen et al., in U.K. Pat. No. 1,570,362 and in Canadian Patent No. 1,105,761 disclose the use of solid particle milling methods such as sand milling, bead milling, dyno milling, and related media, ball, pebble, sand, bead, and roller milling methods for the production of solid particle dispersions of photographic additives such as couplers, UV-absorbers, UV stabilizers, white toners, stabilizers, and sensitizing dyes. These methods further include colloid milling, milling in an attriter, dispersing with ultrasonic energy, and high speed agitation (as disclosed by Onishi et al. in U.S. Pat. No. 4,474,872 and incorporated herein by reference). Details about these methods of milling may be found in Paint Flow and Pigment Dispersions by Temple C. Patton, published by John Wiley & Sons (New York; 1979), in Chapters 17-24 on pages 376-500.
Bagchi, in U.S. Pat. Nos. 4,970,139 and 5,089,380, discloses methods of preparing precipitated coupler dispersion with increased photographic activity. Said methods comprise steps to simultaneously precipitate hydrophobic couplers in the form of small particles and wherein said particles incorporate at their instant of formation water insoluble coupler solvents.
Young et al., in International Application WO 92/06411, disclose that couplers tend to be present as a supersaturated solution in an oily solvent and teach that additives may be added to delay or prevent crystallization. Mader et al., in Offenlegungsschrift DE 4,000,844 A1, disclose that certain non-diffusing yellow couplers are difficult to dissolve in solvents such as tricresyl phosphate and readily form crystalline precipitates to form coating defects and point defects. Such crystallization in dispersion making is known to result from crystals that are large enough to cause optical scattering problems, viscosity problems, and coating defects. Typically, such problem crystallites are known to be greater than 5-30 .mu.m in largest dimension. It is known, on the other hand, that dispersions of nanocrystalline materials less than 1,000 nm in largest dimension do not scatter unduly, and generally are not problematic in coating melts or in liquid dispersion.
Chari et al., in U.S. Pat. No. 5,008,179, disclose the preparation of amorphous coupler dispersions by pH and solvent shifting and the mixing of said coupler dispersions with dispersions of permanent solvent immediately prior to preparing light sensitive coating melts. This process of combining permanent solvent with amorphous coupler dispersion minimizes certain difficulties arising from crystallization of said coupler during storage of the coupler dispersion. Chari et al. disclose the preparation of permanent solvent dispersions wherein the permanent solvent is loaded into a polymeric latex.
Kuhrt et al. in German Patent No. DD 299 608 disclose methods of preparing dispersions, and point out that nanoamorphous dispersions prepared with solvents are unstable and will coalesce on storage.
Czekai and Bishop, in U.S. Pat. No. 5,110,717, disclose the preparation of amorphous particles by first providing a microcrystalline dispersion of particles, raising the temperature of the dispersion above the melting point of the crystalline material, and cooling the dispersion to form amorphous particles.
Karino et al., in European Patent Application EP 0 554 834 A2, disclose methods for dispersing filter dyes for photographic applications. In particular, Karino et al. disclose heating processes for photographic filter dye materials and for nanocrystalline filter dye dispersions, and describe the effects of such heating on the resulting optical absorption of such dye materials. Karino et al. disclose that the molecular orientation of filter dyes in the form of solid particle dispersions may be modified by heat treatment, mechanical treatment, and high frequency treatment. These changes in molecular orientation have been correlated with changes in the visible absorption spectra of the corresponding dyes. Karino et al. disclose various thermal and chemical annealing processes for crystalline dye materials. Oppenheimer, in European Patent Application EP 0 555 923 A2, discloses that the formation of crystals in dispersions can interfere with the functioning of the dispersion, the coatability of the dispersion, and the optical properties of the dispersion, and that it is desirable to suppress crystal formation in photographic dispersions.
Texter, in European Patent Application EP 0 590 567 A1 and in U.S. Pat. No. 5,401,623, discloses the formation of microcrystalline coupler dispersions and the control of coupling reactivity by admixture with coupler solvents.